<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>closest</title>
    </head>

    <body>
        <p>
        <div id="div-01">Here is div-01
            <div id="div-02">Here is div-02
                <div id="div-03">Here is div-03</div>
            </div>
        </div>
        </p>
       <script type="text/javascript" src="closest.js"></script>
    </body>
</html>